Not applicable.
Not applicable.
1. Field of the Invention
The present invention generally relates to cooling a computer system. More particularly, the present invention relates to controlling a fan speed to cool a computer system. Still more particularly, the invention relates to a fan speed controller which slowly adjusts a speed of a fan to reduce the audible perceptibility of the speed change.
2. Background of the Invention
Any electrical component that has current flow through it produces heat, and computers are no exception. Heat in a computer system may be tolerable to some degree, but excess heat must be removed from the system to allow the electronic components to function properly. The response to the need to remove the heat from a computer system has in large part been the use of fans.
In the early days of computer technology, when central processing unit (CPU) speeds were low, a small fan running at a relatively low speed was sufficient to remove excess heat from the computer system. As computer system technology advances and microprocessor speeds increase, more excess heat is generated within a computer system that must be removed. Computer system designers have resorted to increased number of fans, larger fans, and fans having higher speeds. Indeed, given the present state of the art in computer system design, many CPU""s have a dedicated fan to thermally cool just the CPU, and the computer system itself has a second fan to cool the remaining components.
As the number of fans and fan speeds has increased, so too has the audible noise associated with these fans. Computer system users are becoming increasingly aware of audible noise associated with their computer system fans. This is especially true of users of desktop computers, which by definition, sit on or near one""s desktop, and laptop computers which may be used remotely on battery power. For obvious reasons, it is undesirable for a user to be distracted by fan noise from the computer.
Computer system designers and computer system users of laptops are also acutely aware of battery life for their systems. The larger a fan or the faster a fan runs affects the amount of power drawn from the laptop""s battery and therefore the fan itself can significantly diminish battery life for laptop computers. Recently, similar concerns for the general conservation of energy have driven computer system manufacturers to find ways to reduce power consumption in desktop computers as well.
The combination of heightened awareness of audible noise associated with computer fans and concerns for energy conservation have driven manufacturers of computer systems to reduce computer system fan speeds when the thermal load in the computer system so allows. That is, when the volume of airflow needed to cool a computer system is less than the volume of airflow that could be moved by a fan operating at full speed, the computer system fan speed is reduced or is completely shut off. Some computers, therefore, have a somewhat variable fan speed control which may be sensitive to temperature detected by temperature sensors. Reduced fan speed not only decreases computer system power consumption but also reduces audible noise levels associated with the speed of the fan.
While computer systems having a variable speed fan control have addressed to some extent the problems of audible noise and power consumption generally, a new problem arises with changing the speed of a fan. FIG. 1 shows a graph plotting desired fan speed as a function of time. Prior to time txe2x80x2, the speed of the fan is set at N. At or near time txe2x80x2, conventional computer system components or software determine that the speed needs to increase to N+3 to shed the computer of excess heat. Having determined that N+3 is the desired speed, such computer systems instantaneously change the fan speed set point from N to the new speed, N+3. Given the increased set point, the computer system fan rapidly changes speed from N to N+3. This change in speed may occur in less than one second. This rapid change in fan speed creates an annoying change in audibly perceptible noise.
Computer system users typically become accustomed to a particular level of background noise, whatever that level happens to be. If the computer system is a desktop having a fan speed set at N, the user may be only subconsciously aware of the background noise associated with the fan. However, it has been found that users become consciously aware of changes in audible noise associated with rapid changes in fan speed. What is needed then is a way to fulfill the goal of having a variable fan speed control that reduces or eliminates the audible annoyance conventional variable speed fans cause.
The problems noted above are solved in large part by a fan control device that slowly adjusts the fan speed from a previous speed of the fan, which constituted a previous thermal balance for the computer system, to a target fan speed, which constitutes a new thermal balance given the current heat load in the computer system.
In the preferred embodiment, a fan controller receives a target fan speed from the CPU over a system management bus. Given the target fan speed, the fan controller adjusts the fan speed output from a previous speed towards the target speed slowly such that the audible signature associated with accelerating or decelerating a fan is minimized and therefore not made perceptible, or at least as perceptible, to the computer system user.